Systems and methods for determining selected exercise resistance

ABSTRACT

A system and method for determining a selected weight in exercise equipment (which may include an incremental weight sensor disposed on a shaft rotatably fastened with an incremental weight selection dial). The weight stack incremental sensor produces an electrical signal related to the dial position. A spring element or plurality of spring elements are disposed between a reference member and an unused portion of a weight stack results in spring displacement during an exercise motion. A weight stack sensor disposed between the reference member and the unused portion of a weight stack produces an electrical signal related to displacement. The sensor electrical signals can be used by an electronics unit to compute the total weight lifted by a user of exercise equipment.

RELATED APPLICATIONS

This application claims the benefit of co-pending U.S. Provisional Patent Application Ser. No. 61/931,679, filed 26 Jan. 2014, and entitled “System and method for determining weight selected in exercise equipment,” which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

This invention relates generally to the field of exercise equipment, and more specifically, systems and methods to enable monitoring selectively variable attributes of such equipment during an exercise motion.

Methods to detect weight lifted by a user of an exercise machine have been disclosed in prior patents and demonstrated in commercially available exercise equipment. Electronic detection of an amount of weight lifted or selected on or in connection with an exercise machine is known to be beneficial to a user of the exercise equipment; for example, the detected weight can be used in an electronic display of real-time fitness feedback to a user (e.g. number of repetitions, number of calories burned per repetition or over a predetermined time, etc.), or for electronically storing a workout history of a user, so that the user is able to conveniently track progress of a specific fitness or therapeutic goal. Specific workout tracking features that combine other sensor information, along with the detected value of selected weight have been demonstrated in commercial products and cited in prior patents. These features include and are not limited to computing work exerted on the weight stack and power exerted on the weight stack by the user of the exercise equipment.

For example, load cells have been used to detect an amount of weight lifted. The load cell is mechanically connected on one end to the weight stack and on the other end to the mechanical cable or belt. The load cell detects both the static value of the selected weight as well as the forces that arise due to motion of the weight stack. Because the load cell is rigidly attached to the mechanical cable of the exercise equipment the electrical wire connection of the load cell must be designed to tolerate the motion of the weight stack, without being damaged, for example, by fatigue. This represents a significant drawback because it is costly to make an electrical wire connection that can reliably tolerate such motions. In addition, accurate load cells are generally expensive transducers, especially load cell types that rely on a strain gage element.

As another example, proximity sensors have been used to detect motion of a weight stack and, with a priori knowledge of the dimensions of the weight stack plates, the weight could be estimated. These techniques exhibit significant delay to compute the weight lifted because often substantial motion must occur before the profile of the selected weight stack is known. These techniques also must be calibrated for every different weight stack attribute, such as a varied dimension of the weight plate. For these reasons, this prior method has significant practical drawbacks.

Non-contact methods of weight detection have also been disclosed. In one embodiment of such arrangement, an electromagnetic wave emitter and receiver are located on a stationary member of the machine and an electromagnetic wave reflecting device is located on the weight selector pin. An electronics unit generates the transmitted signals and processes the received signals to determine the distance of the weight selector pin. Since the weight plates have a known dimension the electronics unit is able to compute the weight selected based upon the distance measurement. An alternative embodiment may use an infrared sensor instead of the electromagnetic sensor. This prior technique may have certain drawbacks, such as use of a unique selector pin. Accordingly, if the weight stack selector pin is lost, which is common, and a generic replacement pin is used the system cannot function properly. Also, the weight stack selector pin provides only a small reflective surface which is difficult to accurately target with a transmitter, resulting in inaccurate measurements of position, especially for pin locations that correspond to a longer distance between the pin and the transmitter.

Another non-contact method uses an optical, or light-based sensor for detecting motion of the weight stack. A light reflector is used on the quasi-stationary (i.e., unused during exercise) portion of the weight stack, which may decrease sensitivity to weight plate dimensions. However, the use of optical sensors can result in sensitivity to dust and dirt build-up, which can cause degraded performance, such as a loss of accuracy, within the lifetime of the exercise equipment. Further, a light emitter and light detector arrangement may have a non-linear characteristic in function of position. This non-linear characteristic depends on many factors such as the light transmitter manufacturing tolerance, the degradation of the photo transmitter with time, and the exact mounting arrangement of the components, thus the technique requires extensive and precise calibration procedure for each sensor installation. Prior optical systems may also require significant electrical power. Increased power consumption is undesirable, for example, if the system is required to function from a source of battery power, solar power, or a source of power other than power mains. Still another drawback of the technique is that very short distance sensing is not well-suited to optical techniques. Time-of-flight measurement techniques are the most robust and common optical distance measurement techniques used, for example in laser distance meters, and are not practical in this arrangement due to the time of flight of the light being too short to measure with sufficient precision.

Accordingly, the art of determining and recording and/or displaying a selective resistance to an exercise motion may benefit from systems and methods that address one or more drawbacks experienced by prior systems and/or methods, or that advance information gathering, tracking, computation and/or display as it relates to exercise machines.

SUMMARY OF THE INVENTION

According to an aspect of an embodiment of an apparatus according to the present invention, such apparatus may include a plurality of weight plates including a bottom weight plate. The weight plates may be at least partially selectively vertically translatable along a translation path from an at-rest position. The apparatus may also include a sensor configured to measure a displacement of the bottom weight plate from the at-rest position. The sensor may include a stationary component and a moveable component, wherein the displacement of the bottom weight plate is automatically measured by sensing two positions of the moveable component with respect to the stationary component. The moveable component may be in physical contact with the stationary component (e.g., if the sensor includes a slide potentiometer) or may be spaced therefrom (e.g., if the sensor includes a magnetic, optical or capacitive encoder). A biasing member (e.g., a spring having a predetermined bias spring constant) may be included as a part of the sensor to bias the moveable component in a first direction into contact with the bottom weight plate. When the weight plates are positioned at the at-rest position, the bottom weight plate may be at least partially supported by a plurality of weight stack springs, each weight stack spring having a spring constant that is at least substantially greater than the spring constant of the biasing spring. If the sensor includes a slide potentiometer, it may include a wiper lever biased by a wiper bias force in a second direction opposite the bias direction of the moveable component, the wiper bias force being substantially less than the predetermined bias spring constant. An electronics unit may be electrically coupled to the sensor, the sensor providing a sense signal to the electronics unit for signal processing. The sense signal may be an analog signal or a digital signal.

According to an additional or alternative aspect of an embodiment of an apparatus according to the present invention, such apparatus may include a plurality of weight plates including a bottom weight plate. The weight plates may be at least partially selectively vertically translatable along a translation path from an at-rest position. The apparatus may further include a plurality of selectable incremental weights, each weighing less than each weight plate. A first sensor may be configured to sense a selection of the incremental weights. The selection of incremental weights may be made using a dial fixed to a shaft. The sensor may be configured to sense a rotational position of the shaft. A second sensor may be configured to measure a displacement of the bottom weight plate from the at-rest position. An electronics unit may be electrically coupled to the first sensor and the second sensor.

The electronics unit may be configured to receive a first sense signal from the first sensor and determine a first amount of selected incremental weight based on the first sense signal. The electronics unit may additionally or alternatively receive a second sense signal from the second sensor and determine an amount of force removed from the bottom plate based on the second sense signal. The electronics unit may be either or further configured to calculate a total lifted weight as the sum of the first amount of selected incremental weight and the amount of force. The electronics unit may be either or further configured to display at least one of the first amount of selected incremental weight, the amount of force, and the total lifted weight. The electronics unit may be either or further configured to start a timer at a start time upon detection of a first change in the second sense signal and stop the timer at a stop time upon detection of a second change in the second sense signal. A calculation may then be made of an exercise duration by subtracting the start time from the stop time. the translation path is at least partially defined by one or more longitudinal guide rods extending through the plurality of weight plates, the apparatus further comprising an electronics unit electrically connected to the first sensor through an electrically conductive path comprising at least a portion of the guide rods.

According to an aspect of an embodiment of a method according to the present invention, the method includes the step of conducting electricity along a conductor, the conductor comprising a portion of a first guide rod, wherein the guide rod comprises a longitudinal rod on an exercise machine, the rod extending through a plurality of weight plates, the weight plates being at least partially selectively translatable along a translation path from an at-rest position. The method may further include the step of sensing a first voltage across a first resistor in electrical communication with the conductor, the second voltage being caused by the conducting step. The method may further include the step of sensing a second voltage across a second resistor in electrical communication with the conductor at a different time than the first resistor, the second voltage being caused by the conducting step. The exercise machine may further include a plurality of selectable incremental weights, each weighing less than each weight plate, the first voltage corresponding to a first selection of the incremental weights and the second voltage corresponding to a second selection of the incremental weights.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a first elevation view of an exemplary exercise machine incorporating embodiments according to the present invention.

FIG. 2 is a second, partial elevation view of the machine of FIG. 1, opposite the view of FIG. 1.

FIG. 3A is a partial assembly elevation view of a first embodiment of a weight stack position sensor according to the present invention.

FIG. 3B is a partial assembly elevation view of a second embodiment of a weight stack position sensor according to the present invention.

FIG. 4 is a schematic view of a first embodiment of a weight stack position sensor according to the present invention.

FIG. 5A is a graphical representation of an exemplary relationship of a weight stack sensor electrical signal and associated mechanical displacement.

FIG. 5B is a graphical representation, in the time domain, of the weight stack sensor electrical signal during an exercise motion.

FIG. 6 is a partial cross-section view taken along line 6-6 in FIG. 2.

FIG. 7A is a first partial cross-section view taken along line 7-7 of FIG. 6.

FIG. 7B is a second partial cross-section view taken along line 7-7 of FIG. 6.

FIG. 8A is an electrical schematic for a first embodiment of an incremental weight sensor according to the present invention.

FIG. 8B is an electrical schematic for a second embodiment of an incremental weight sensor according to the present invention.

FIG. 8C is an electrical schematic for a third embodiment of an incremental weight sensor according to the present invention.

FIG. 8D is a graphical representation of the incremental weight stack sensor electrical signal relative to a rotary position of an incremental selector dial.

FIG. 9 is a block diagram electrical schematic representation of a signal processing arrangement of a weight stack sensor and incremental weight sensor according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Although the disclosure hereof is detailed and exact to enable those skilled in the art to practice the invention, the physical embodiments herein disclosed merely exemplify the invention which may be embodied in other specific structures. While the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims.

Turning now to the Figures, FIGS. 1 and 2 present an embodiment 100 of an exercise machine, or piece of exercise equipment, which may include embodiments of systems according to the present invention. The exercise equipment 100 preferably includes a selective resistance, such as a weight stack 110 having a plurality of weight plates 112, including a top weight plate 112 t and a bottom weight plate 112 b. Unselected or at-rest weight plates 112 rest on a plurality of springs 114 disposed vertically beneath the weight stack 110, such as between the bottom weight plate 112 b and a lower frame member 116 of the exercise equipment 100. The selected load plates 112 of the weight stack 110 translate along a path defined at least partially by one or more guide rods 118, which in one embodiment may include a first guide rod 118 a and a second guide rod 118 b. The guide rods 118 typically have a substantially circular cross sectional shape. The weight stack 110 may interface to the guide rods 118 through a plurality of bearings 120 which may be fastened on the top weight plate 112 t and at least partially circumferentially disposed around guide rods 118. The guide rods 118 typically extend vertically between the lower frame member 116, located below the weight stack 110, and an upper frame member 117 located above the weight stack 110. Generally, each guide rod 118 is preferably constructed from a conductive guide rod member 119, e.g., a first guide rod conducting member shown in FIG. 2A, having a low electrical resistivity material property, which may include a common steel or steel alloy. Each guide rod 118 may further include or support an insulating guide rod member 121, having a high electrical resistivity material property, for example, a high strength plastic. The insulating member 121 may be adapted to prevent electrically conductive contact between the rod 118 and any of the weight stack plates 112. Each end of each guide rod 118 may be mechanically secured to each of the lower frame member 116 and the upper frame member 117 by a guide rod seat 123 The guide rod seat 123 is preferably constructed of a material having a substantially insulative electrical property, for example a plastic polymer, PVC, or rubber.

The exercise machine 100 may further include an incremental weight stack assembly 150, which may be fastened to the top weight plate 112 t of the weight stack 110. The incremental weight stack assembly 150, as is generally known in the art, preferably comprises a plurality of incremental weights 152, the incremental weights 152 having a weight measurement that is typically less than the weight of a single weight plate 112. For example a weight plate 112 may have a nominal weight of about twenty pounds, whereas each incremental weight 152 may have a lower nominal weight, such as a factor of the nominal weight of the weight plate 112 (e.g., one pound, two pounds, two-and-a-half pounds, four pounds, five pounds, or ten pounds). The incremental weights 152 are guided by an incremental weight guide track 154 and are typically not supported by the weight stack springs 114. The incremental weight stack assembly 150 further comprises a weight selector dial 156 rotatably supported by a shaft 158, the shaft 158 rotatably fastened to a selector mechanism 160 (see FIG. 6). The selector mechanism 160 is mechanically coupled to a plurality of selector rods 162, which engage the proper incremental weight plates 152, according to the position of the incremental weight selection dial 156. Incremental weight selection apparatus are utilized by several manufacturers and are pervasive in modern exercise equipment. A variety of incremental weight stack apparatus 150 are employed in the industry to accomplish the similar function. The incremental weight selection assembly 150 provided in FIGS. 2A, 2B, 2C, and 2D of the present disclosure are intended for exemplary purposes only and should not be viewed as a limitation of the present invention. The incremental weight selection assembly 150 is intentionally depicted in a simplified form to better illustrate the function and advantages of embodiments of systems and methods according to the present invention.

According an embodiment of the present invention, a weight stack sensor 200 may be coupled to or form a portion of the exercise machine 100. Referring more particularly to FIG. 3A, the weight stack sensor 200 may be in electrical communication with an electronics unit 300, such as by a weight stack sensor electrical cord 302, comprising a plurality of signal and supply wires. Generally, the weight stack sensor 200 is disposed between the bottom plate 112 b of the weight stack 110 and a reference member, such as the lower frame member 116. The weight stack position sensor 200 has two members that move with respect to one another, which may include a stationary member 210 and a moving member 250.

The stationary member 210 preferably includes a housing 211 affixed to the reference member, such as the lower frame member 116. The housing 211 may be substantially closed to assist in maintaining a clean sensor arrangement, or it may be provided in an open frame or truss structure. The housing 211 generally provides structural support for the sensor 200.

The moving member 250, such as a plunger 252, preferably extends through the housing 211 and is biased longitudinally outward therefrom by a biasing member 254, such as a coil spring 256. The biasing member 254 may be compressed between the plunger 252 and the housing 211, or the biasing member 254 may extend through the housing 211 and be compressed between the plunger 252 and the reference member (e.g., bottom frame member 116). The plunger 252 has a distal end 252 a, which is adapted to contact a portion of the weight stack 110, such as the bottom plate 112 b. Alternatively, the plunger 252 distal end 252 a may be affixed to the weight stack 110. The weight stack position sensor stationary member 210 includes a guide bearing 212 to direct a sliding movement of the moving member 250.

In one embodiment of the present invention, the weight stack spring 114 has a known characteristic, k_(s), that relates the spring displacement, x, and the spring force, F_(s), according to the following equation:

F _(s) =k _(s) x   (EQ 1)

While the bias spring 256 could be the same as the weight stack springs 114, it is preferred to utilize a bias spring 256 that has a spring constant that is significantly less than the spring constant k_(s) of the weight stack springs 114, such that the function of the spring 256 is primarily to maintain the plunger 252 biased vertically upward and to overcome any opposing bias of a sensing element 220, as described below. Herein, the spring characteristic of a weight stack spring 114 is referred to as the spring constant, k_(s), and is assumed to be constant for convenience in clearly describing the present invention. Those who are skilled in the art will recognize that the spring constant k_(s) may also be a non-linear coefficient, having a characteristic that changes as a function of spring displacement, without departing from the scope and intent of the present invention. Those who are skilled in the art will also recognize that any variety of spring types and springs constructed of various materials may be applied without departing from the scope and intent of the present invention. Spring types that may be used for the weight stack springs 114 or the plunger bias member 254 include but are not limited to coil springs, conical coil springs, elastomer springs, air springs, gas-filled springs, and/or rubber or polymer springs.

The position sensor 200 has a means of accurately detecting a position of the moving member 250 relative to the stationary member 210. Detection may be accomplished with a sensing element 220 and a means of producing an electrical signal, which is deterministically related to the position of the moving member 250, relative to the stationary member 210. In one embodiment (see FIG. 4) of the present invention the weight stack position sensor sensing element 220 incorporates an electrical potentiometer 222, comprising a three terminal resistive element, a first terminal 224 connected to a voltage supply 325, a second terminal 226 connected to a voltage supply return. A third, wiper terminal 228, is electrically connected to a wiper 230 (moveable by a wiper lever 232, which is preferably biased downwardly against a wiper lever seat 253 provided on the plunger 252), which creates a voltage divider, providing a position indication, such as a sense voltage SV, to the electronics unit 300. The sense voltage SV is typically less than or equal to the voltage of the voltage supply 325, and is generally proportional to the displacement of the sensor plunger 252. The weight stack sensor 200 is electrically connected to the electronics unit 300 via the weight stack sensor electrical cord 302 comprising a plurality of wires. The electronics unit 300 is capable of computing parameters, including, e.g., an amount of weight lifted and/or a time of a weight lifting exercise, based upon the sense voltage SV. While the position indication is preferably a voltage, it may also be a current, or a digital communication message if the sensor 200 is equipped with an appropriate apparatus. The position sensor moving member 250 is firmly attached to the wiper lever 232, which moves responsive to and preferably in direct proportion to the movement of the position sensor moving member 250.

Those who are skilled in the art will recognize that a variety of techniques may be used as the position sensing element 220, without departing from the scope and intent of the present invention. Referring to FIG. 3B, for example, an exemplary alternative position sensor 400 is shown, where like reference numerals refer to at least substantially similar or identical structure having similar function as those elements of the embodiment of FIG. 3A, except where otherwise indicated. Rather than contact the plunger 452, however, this embodiment 400 includes a non-contact sensor element 420, including a magnetic encoder strip 458 disposed on the plunger 452 and a magnetic sensor read head 460 disposed substantially orthogonally to, and spaced by a suitable read gap 462 from, the strip 458. Other sensing element types include both contact types and non-contact types and include but are not limited to ultrasonic sensors, magnetic sensors and encoders, capacitive sensors and encoders, and optical sensors and encoders.

Referring now also to FIG. 5A and FIG. 5B, the function of the weight stack position sensor 200 may be more fully explored. Prior to a user initiating an exercise motion, a weight stack 110 comprising a plurality of weight plates 112 rests on a plurality of springs 114. The springs 114 are compressed according to a combined spring constant of the plurality of springs 114, for example, for the case of n springs with a spring constant k_(s), the combined spring constant k_(c) can be computed according to the following equation:

k _(c) =n*k _(s)   (EQ 2)

The position sensor 200 produces a first sense voltage SV₀, representing a first position WS₀ of the sensor moving member 250, relative to the position sensor stationary member 210. Referring to FIG. 5A, when a user performs an exercise motion (e.g., at least some of the weight stack 110 is displaced), the bottom weight plate 112 _(b) displaces by an amount determined by the combined spring constant, k_(c), and the position sensor produces a second sense voltage S₁, representing a second position WS₁ of the position sensor moving member 250, relative to the sensor stationary member 210. Herein, the change in position of the position sensor moving member 250, relative to the stationary member 210, due to an exercise motion will be referred to as the sensor displacement. In one embodiment of the present invention, referring to FIG. 5A, the sense voltage SV changes in direct proportion with the sensor displacement, and therefore changes in direct proportion to the weight lifted by the user.

The sense voltage SV may be used to determine the amount of weight lifted off of the stack 110. Referring to FIG. 9, an electronics unit 300, comprising an analog-to-digital converter, a microcontroller, and memory is able to store in non-volatile memory a previously calibrated value of the combined spring constant, k_(c). The memory may also be used to store calculated parameters and log usage of the exercise machine 100. The electronics unit 300, having monitored a scaled electrical signal x_(e) proportional to the sensed voltage SV, is able to use the signal x_(e) as received from the sensor 200 or convert the scaled electrical signal x_(e) to a digital word for signal processing, typically by a microcontroller. The electronics unit 300 is able to compute the weight, F, defined in units of force (for example, Lbs-Force in English units or Newtons in SI units), according to Equation 3 (EQ 3). The electronics unit 300 can also compute the mass of the weight lifted from the stack, M_(wsl), according to Equations 3 (EQ 3) and 4 (EQ 4):

F=k _(c) *x _(e)   (EQ 3)

M _(wsl) =M _(ws) −F/g   (EQ 4)

In EQ 4 the constant, g, represents the acceleration due to gravity and has a typical value of g=9.81 m/s² at the surface of the earth. In EQ 4 the weight stack mass M_(ws) is the mass supported by the springs 114. Depending on the design of the incremental weight selector assembly 150, the weight stack mass M_(ws) may also include the mass of the incremental weights 152 and or the assembly 150. To reiterate, the combined spring constant, k_(c), may also be a non-linear coefficient, having a characteristic that changes as a function of spring displacement. Those who are skilled in the art will appreciate that a non-linear characteristic can be processed by the electronics unit 300, typically within a microcontroller and can still be effective for determining the weight and/or mass lifted by the user.

When a user completes an exercise motion, sometimes referred to as an exercise set, the entire weight stack 110 is resting on the springs 114. The springs 114 are compressed, according to the combined spring constant k_(c) and the corresponding sensor displacement (WS₁−WS₀) is calculated by the electronics unit 300. In FIG. 5B, an exemplary waveform of the sense voltage SV during an exercise motion is provided. The sense voltage SV has a first electrical signal value SV₀, associated with the position of the weight stack 110 when it is in a rest position, and a second electrical signal value SV₁, associated with an exercise motion (e.g., at time period during which a portion of the weight stack 110 has been removed from contact with the remainder of the weight stack 110, the remainder including the bottom weight plate 112 _(b), or during which the entire weight stack 110 has been removed from contact with the springs 114). The waveform in FIG. 5B is representative of an exercise in which a portion of the weight stack 110 is lifted and the weight thereof is not transferred back to the springs 114 until the exercise is complete. In an alternative exercise, at least a portion of the amount of weight of a lifted portion of the weight stack 110 may be transferred to the springs 114, in which case oscillations may occur in the sensed voltage SV throughout a set of exercise repetitions. In one embodiment of the present invention, the weight stack sensor displacement detected by the electronics unit 300 is used to determine the occurrence of initial exercise motion, the occurrence of a completed exercise motion, and the duration of the exercise motion.

In another embodiment, alone or in combination with the weight stack sensor 100, an incremental weight sensor 500 may be connected to the electronics unit 300 and scaled electrical signals associated therewith may be created in the electronics unit 300. The incremental weight sensor 500 is preferably electrically connected to the electronics unit 300, at least in part, by the guide rods 118. A first guide rod conducting member 502 is electrically connected in series with an incremental sensor electrical cord 504, comprising one or a plurality of signal and supply wires. The first guide rod conducting member 502 may be electrically connected with the cord 504 through the bearing, as later described. A second guide rod conducting member 506 is electrically connected in series with an incremental sensor supply cord 508, comprising one or a plurality of signal and supply wires.

Referring to FIG. 6, in one embodiment of the present invention, a position sensing means, preferably a multi-position electrical switch 510 is rotatably coupled to the incremental weight selector assembly 150, preferably being mounted to the rotating shaft 158. In this arrangement, a rotary position of the switch 510 generally relates directly to the rotary position of the incremental selector dial 156, as depicted in FIG. 8D. For example, a first incremental dial rotary position D₁ corresponds to a first rotary position of the multi-position electrical switch 510, and a second incremental dial rotary position D₂ corresponds to a second rotary position of the multi-position electrical switch 510, and so on. Referring again to FIG. 6, a sensor supply wire 550 is electrically connected to a first bearing 552 and the multi-position electrical switch 510, preferably the pole 512 of the switch 510. A plurality of throw terminals 514 of the multi-position electrical switch 510 may be connected electrically to a plurality of passive impedance elements 516, for example, resistors, by a plurality of electrical wires 518. The resistors may be mounted to a resistor PCB assembly 520, in turn, the resistor PCB assembly 520 is fastened to a translating member of the exercise equipment 100, for example, the incremental weight selector assembly 150 or the top weight plate 112 t. A incremental sensor signal wire 554 is electrically connected to an electrically a second bearing 556 and may further be connected to the plurality of passive impedance elements 516, for example resistors, that may be mounted to the resistor PCB assembly 520. The amount of electrical current flowing in the incremental sensor supply wire 550 is preferably substantially the same as the electrical current flowing in the incremental sensor signal wire 554.

Pertaining to the incremental weight sensor 500, other sensing means may be applied and fall within the scope of the present invention. For example, an electrical potentiometer rotatably coupled to the shaft 158 may be used in place of the multi-position electrical switch 510 and a portion of or all of the impedance elements. Other incremental weight sensing means are generally contemplated and include and are not limited to potentiometers, encoders, and proximity sensors. Other sensor arrangements disposed on other mechanical members of the incremental weight stack assembly 150, for example, the incremental selector rods 162 are also contemplated in the present disclosure.

As previously indicated, the switch 510 is preferably electrically coupled to the electronics unit 300 through the guide rods 118, preferably through a conductive bearing disposed on each guide rod 118. Referring now to FIG. 7A, a first embodiment 600 of a conductive bearing is shown. The bearing 600 preferably includes a number of elements commonly known to bearings and in particular linear bearings, including a plurality of ball bearings 602, one or more ball bearing tracks 604, sometimes referred to as bearing raceways or channels, a dust cover or wiper 606 or plurality of wipers 606 (which may be electrically conductive), and a bearing housing 608. The elements of the bearing are preferably constructed of an electrically conductive material, such as a metallic material. The plurality of ball bearings 602 are in mechanical contact (i.e. rolling frictional contact) with the guide rod conducting member 502 or 506, and may form an electrically conductive path, preferably having low electrical impedance, through which an electrical current may flow. For example, an impedance of less than 1,000 Ohms (1 kΩ) between a bearing housing 608 and a guide rod conducting member 502 or 506. The electrically conductive path may have a substantially resistive, capacitive, or inductive impedance characteristic, or some combination thereof. The bearing 600 is mounted to the top weight plate 112 t via a bearing insulator 610. The bearing insulator 610 forms a substantially high electrical impedance between the bearing housing 608 and the top weight plate 112 t, for example, an impedance greater than 10 MΩ of resistance between the bearing housing 608 and the top weight plate 112 t. As indicated above, the guide rod 118 may have or support an additional guide rod insulating member 121 that comprises an electrically insulating material, for example a high strength polymer, that has a large electrical resistivity property. The interface between the guide rod insulating member 121 and the guide rod conductive member 502 or 506 can be located anywhere along the length of the guide rod 118; as one example, the interface may be located substantially at the center of the thickness of top weight plate 112 t when the weight stack 110 is in the at-rest position as depicted in FIG. 2C and FIG. 2D. In an alternative embodiment of the present invention, the guide rod 118 may only comprise a guide rod conductive member 502 or 506, without the insulating member 121. As already described in the present disclosure, the guide rod ends are mechanically located via guide rod seats 123 that have an electrically insulating material property.

Those who are skilled in the art will recognize that a variety of bearing types may be used without departing from the scope and intent of the present invention. Bearing types include and are not limited to linear bearings, sleeve bearings, slide bearings, and various arrangements of these and other bearings. FIG. 7B illustrates an alternative embodiment 700 of the present invention wherein a sleeve bearing 702 is utilized instead of ball bearings 602. Regardless of the bearings used, an electrically conductive path is established preferably from a power supply 570, through the supply cord 504, through the first rod 118 a, through a first bearing frictional member (e.g. ball bearings 602), through a first bearing housing (e.g. 608), through the supply wire 550 (which may be secured to the housing with a screw), through the switch 510 and PCB 520 (or other sensor and/or related circuit), through the signal wire 554, through a second bearing housing (e.g. 608), a second bearing frictional member (e.g. ball bearings 602), through the second rod 118 b, and through the signal cord 508.

Referring to FIG. 8A, an electrical schematic of a preferred embodiment of the incremental weight sensor 500 is illustrated, also depicting the equivalent electrical attributes of the bearings 602. An incremental sensor electrical supply 570 is established, typically by the electronics unit 300. The supply 570 is typically a DC (FIG. 8A) or AC (FIG. 8B) voltage source supply, but may alternatively be an AC or DC current source supply. A complete electrical circuit network is formed by the incremental sensor supply 570, the multi-position electrical switch 510, a first resistor 516 a connected to a first switch throw 514 a, a second resistor 516 b connected to a second switch throw 514 b, and a third resistor 516 c connected to a third switch throw 514 c, and a termination resistor 572. A fourth switch throw 514 d may be left as open circuit. Circuitry within the electronics unit 300 measures the signal, typically a voltage, across the termination resistor 572. In FIG. 8A the electrical effect of the bearings 602 are represented by an equivalent bearing contact resistance 530. The value of the sensor resistors 516 and termination resistor 572 and other impedances that may be employed are preferably selected to be much greater than the value of the bearing contact resistance 530.

Referring again to FIG. 8A, the electrical connection of the first sensor resistor 516 a connected to the switch pole 512 by the first switch throw 514 a corresponds to a first mechanical position of the multi-position electrical switch 510. As previously described in the present disclosure, a first mechanical position of the multi-position electrical switch 510 corresponds to a first mechanical position of the incremental weight selector dial 156. Referring now to the graph of FIG. 8D, a resulting deterministic relationship exists between the rotary position of the incremental weight selector dial 156 and an incremental sensor scaled electrical signal created in the electronics unit 300 from the voltage developed across the termination resistor 572. A first incremental sensor electrical signal level SL₁ is created for a first rotary position D₁ of the incremental weight selector dial 156, a second incremental sensor electrical signal level SL₂ is created for a second rotary dial position D₂, a third incremental sensor electrical signal level SL₃ is created for a third rotary dial position D₃, and finally a fourth incremental sensor electrical signal level SL₄ is created for a fourth rotary dial position D₄. The sensor resistors 516 are preferably selected such that the first incremental sensor electrical signal level SL₁, a second incremental sensor electrical signal level SL₂, a third incremental sensor electrical signal level SL₃, and a fourth incremental sensor electrical signal level SL₄ have substantially different values. The electronics unit 300 can readily measure and compute the incremental weight selected by employing well-known ADC circuits and digital signal processing techniques.

In one embodiment of the present invention, the multi-position electrical switch 510 comprises a single pole 512, four throw 514 type switch. As previously stated in the present disclosure, and reiterated now, the switch type should not be considered as a limitation of the present invention. Those skilled in the art will readily recognize that there are a variety of switch types and switch arrangements that may be applied and remain within the scope and intent of the present invention. For example, in an exercise machine 100 comprising only two incremental weights (and therefore a selection dial with three positions), a single pole, triple throw switch may be a more appropriate switch type.

The incremental weight sensor 500 may comprise a variety of alternative sensing elements and arrangements without departing from the scope and intent of the present invention. These include and are not limited to rotary and linear potentiometers, rotary and linear proximity sensors, rotary and linear encoders, and accelerometers employing a variety of sensing technologies.

In an alternative embodiment 500′ of an incremental sensor according to the present invention, referring to FIG. 8B, the electrical effect of the bearing 600 or 700 may be better represented by a bearing capacitance 540, and the incremental sensor supply 570 is preferably an AC supply having a substantially high frequency characteristic, for example, a frequency greater than 10 kHz. Lower frequency supplies may also be used.

In FIG. 8C, an alternative embodiment 500″ of the present invention is depicted, wherein the incremental weight sensor comprises a plurality of proximity sensors 510″ preferably coupled to the shaft 158.

Referring to FIG. 9, the electronics unit 300 is capable of computing parameters as discussed herein, based upon the weight stack sensor sense voltage SV and/or the incremental electrical signal level SL. Generally, the electronics unit 300 comprises circuits for processing sensor signals, and typically includes analog and digital gain circuits, analog-to-digital conversion circuits, microprocessors or DSP's, memory, displays including but not limited to LCD and LED displays, wireless communication devices, and other digital and analog circuitry. The electronics unit 300 may be dedicated to the function of determining weight lifted and, more generally, the electronics unit 300 referred to in this invention pertains to an electronic feedback system, and can be used for multiple functions in addition to processing the sensor electrical signals and computing the incremental weight selected and/or the amount of weight of the portion of the weight stack 110 lifted by the user.

Referring now to FIG. 9, the electronics unit 300 preferably computes each of the incremental weight selected and/or the weight stack lifted weight, and further computes the mass of the total weight lifted, M_(tot), by computing the sum of the computed mass of the weight stack lifted, M_(wsl), (previously described in the present disclosure) and the computed mass of the incremental weight, M_(inc), according to Equation 5 (EQ 5).

M _(tot) =M _(wsl) M _(inc)   (EQ 5)

With the total mass of the weight lifted known, the total weight or force (e.g., in units of Lbs) can also be computed by the electronics unit by simply multiplying the total mass by the gravitational constant, g, discussed above. In an alternative embodiment of the present disclosure, sensing elements generally known for motion sensing, for example, accelerometers, and electronic circuits located on the weight stack members are powered from the electronics unit 300. Electronic circuits on the weight stack 110 (such as in the incremental weight selector 150) or in the electronics unit 300 may generally further comprise wireless communication devices for transmitting data wirelessly to one or a plurality of receiving devices or network nodes, such as local area network (LAN) nodes.

The foregoing is considered as illustrative only of the principles of the invention. Furthermore, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described. While the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims. 

I claim:
 1. An apparatus comprising: a plurality of weight plates including a bottom weight plate, the weight plates being at least partially selectively vertically translatable along a translation path from an at-rest position; and a sensor configured to measure a displacement of the bottom weight plate from the at-rest position.
 2. An apparatus according to claim 1, wherein the sensor comprises a stationary component and a moveable component, wherein the displacement of the bottom weight plate is automatically measured by sensing two positions of the moveable component with respect to the stationary component.
 3. An apparatus according to claim 2, the sensor further comprising a biasing member to bias the moveable component in a first direction into contact with the bottom weight plate.
 4. An apparatus according to claim 3, wherein the biasing member is a biasing spring having a predetermined bias spring constant.
 5. An apparatus according to claim 4, wherein when the weight plates are positioned at the at-rest position, the bottom weight plate is at least partially supported by a plurality of weight stack springs, each weight stack spring having a spring constant that is at least substantially greater than the spring constant of the biasing spring.
 6. An apparatus according to claim 5, wherein the moveable component makes physical contact with the stationary component.
 7. An apparatus according to claim 6, wherein the sensor comprises a slide potentiometer.
 8. An apparatus according to claim 7, wherein the slide potentiometer comprises a wiper lever biased by a wiper bias force in a second direction opposite the first direction, the wiper bias force being substantially less than the predetermined bias spring constant.
 9. An apparatus according to claim 5, wherein the moveable component is spaced from the stationary component.
 10. An apparatus according to claim 9, wherein the sensor comprises a linear magnetic encoder.
 11. An apparatus according to claim 9, wherein the sensor comprises a linear optical encoder.
 12. An apparatus according to claim 9, wherein the sensor comprises a capacitive encoder.
 13. An apparatus according to claim 2, further comprising an electronics unit electrically coupled to the sensor, the sensor providing a sense signal to the electronics unit for signal processing.
 14. An apparatus according to claim 13, wherein the sense signal comprises an analog signal.
 15. An apparatus according to claim 13, wherein the sense signal comprises a digital signal.
 16. An apparatus comprising: a plurality of weight plates including a bottom weight plate, the weight plates being at least partially selectively vertically translatable along a translation path from an at-rest position; a plurality of selectable incremental weights, each weighing less than each weight plate; and a first sensor configured to sense a selection of the incremental weights.
 17. An apparatus according to claim 16, wherein the selection was made using a dial fixed to a shaft.
 18. An apparatus according to claim 17, wherein the first sensor is configured to sense a rotational position of the shaft.
 19. An apparatus according to claim 18, further comprising: a second sensor configured to measure a displacement of the bottom weight plate from the at-rest position.
 20. An apparatus according to claim 19, further comprising an electronics unit electrically coupled to the first sensor and the second sensor.
 21. An apparatus according to claim 20, wherein the electronics unit is configured to: receive a first sense signal from the first sensor; determine a first amount of selected incremental weight based on the first sense signal; receive a second sense signal from the second sensor; and determine an amount of force removed from the bottom plate based on the second sense signal.
 22. An apparatus according to claim 21, wherein the electronics unit is further configured to calculate a total lifted weight as the sum of the first amount of selected incremental weight and the amount of force.
 23. An apparatus according to claim 22, wherein the electronics unit is further configured to display at least one of the first amount of selected incremental weight, the amount of force, and the total lifted weight.
 24. An apparatus according to claim 21, wherein the electronics unit is further configured to: start a timer at a start time upon detection of a first change in the second sense signal; stop the timer at a stop time upon detection of a second change in the second sense signal; and calculate an exercise duration by subtracting the start time from the stop time.
 25. An apparatus according to claim 16, wherein the translation path is at least partially defined by one or more longitudinal guide rods extending through the plurality of weight plates, the apparatus further comprising an electronics unit electrically connected to the first sensor through an electrically conductive path comprising at least a portion of the guide rods.
 26. A method comprising the step of: conducting electricity along a conductor, the conductor comprising a portion of a first guide rod, wherein the guide rod comprises a longitudinal rod on an exercise machine, the rod extending through a plurality of weight plates, the weight plates being at least partially selectively translatable along a translation path from an at-rest position.
 27. A method according to claim 26, further comprising the step of sensing a first voltage across a first resistor in electrical communication with the conductor, the second voltage being caused by the conducting step.
 28. A method according to claim 27, further comprising the step of sensing a second voltage across a second resistor in electrical communication with the conductor at a different time than the first resistor, the second voltage being caused by the conducting step.
 29. A method according to claim 28, wherein the exercise machine further comprises a plurality of selectable incremental weights, each weighing less than each weight plate, and further wherein the first voltage corresponds to a first selection of the incremental weights and the second voltage corresponds to a second selection of the incremental weights. 